Question

The sum of first 25 odd natural numbers is _________.

Answer 1

Sum of for 25 odd numbers :-
Let S denote the sum of first 25 odd numbers
Here number are 1, 3, 5, 7, 9 --------- 49.
Here first term is 1

last term is 49

Common difference d is 2
n = 25
$\begin{array}{rcl}\mathrm{i}.\mathrm{e}\mathrm{Sum}& =& \frac{n}{2}\left(a+T_n\right)\\ & =& \frac{25}{2}\left(1+49\right)\\ & =& \frac{25\times 50}{2}\\ & =& 25\times 25\\ & & \end{array}$
i.e sum of first 25 odd numbers = 625.